Effect of Passive Range of Motion Exercises on Lower-Extremity Goniometric Measurements of Adults With Cerebral Palsy: A Single-Subject Design

Sherri LCadenhead, Irene RMcEwen, David MThompson

Published July 2002

Sherri L Cadenhead

SL Cadenhead, PT, MS, PCS, is Early Interventionist, Programs for Infants and Children, Anchorage, Ala. At the time the study was conducted, she was employed at the Northern Oklahoma Resource Center, Enid, Okla

Abstract

Background and Purpose. People with spastic cerebral palsy often receive passive stretching that is intended to maintain or increase joint passive range of motion (PROM) even though the effectiveness of these exercises has not been definitively demonstrated. The purpose of this study was to determine the effect of PROM exercises on 6 adults with spastic quadriplegia and contractures. Participants. Four men and 2 women (X̄=31 years of age, range=20–44 years) who lived in an institution for people with mental retardation participated in the study. Methods. The authors used 2 multiple baseline designs. Three participants (group 1) received lower-extremity PROM exercises during phase A; PROM exercises were discontinued during phase B. Three participants (group 2) did not receive PROM exercises during phase A; PROM exercises were initiated during phase B. Data were analyzed using visual analysis and the C statistic. Results. Results varied with the method of analysis; however, phase A and phase B measurements, overall, did not differ for either group. Discussion and Conclusion. This study demonstrated use of a single-subject design to measure the effect of PROM exercises on adults with cerebral palsy. The authors concluded that the PROM exercise protocol did not have an effect on the lower-extremity goniometric measurements of the participants.

Contractures are among the most common secondary impairments associated with cerebral palsy, particularly for people with the spastic type of cerebral palsy.1Contracture, as it relates to cerebral palsy, has been defined in several ways, including permanent contraction of a muscle,2 high resistance to passive stretch,2 hypoextensibility,3,4 diminished range of passive stretch,5 and intrinsic muscle shortening that prevents full range of motion.6 Many interrelated factors have been proposed to cause contractures in people with cerebral palsy, including more activation of muscles on one side of a joint than on the other side,4 changes in connective tissue and muscle length,7,8 slow muscle growth,4 and positioning.9 People with spastic cerebral palsy who do not walk and whose voluntary movement is restricted to the extent that they cannot independently move their joints through the full range of motion during daily activities are at particularly high risk for developing a contracture.10

Passive stretching is one physical therapy intervention for the prevention or reduction of contractures associated with cerebral palsy.10,11 In our experience, clinicians frequently advocate a prolonged stretch, with the rationale based in part on a classic study by Tardieu et al.5 Tardieu and colleagues measured the amount of time that the soleus muscles of children with cerebral palsy were elongated beyond a minimum threshold length throughout each day. After 7 months, contractures increased in participants whose soleus muscle was elongated for only 2 hours per day, but these contractures did not increase in participants whose soleus muscle was elongated for at least 6 hours a day.

Casting12 and splinting13,14 are 2 interventions that provide a prolonged stretch and have been shown to be effective in preventing or reducing knee and ankle contractures in children with cerebral palsy. Positioning, such as lying prone, standing in standers,15 and sitting with the hips abducted,16 also can provide a prolonged stretch. The effectiveness of most positioning for maintaining or increasing range of motion of people with cerebral palsy, however, has not been studied.15,17 Researchers have shown that using a chair to provide a 5- to 7-hour adductor stretch per day, along with 1 to 3 therapy sessions per week for “progressive manual stretching,”16(p984) did prevent adductor muscle contractures in children with cerebral palsy.

A practical problem associated with providing a prolonged stretch using splints, casts, or positioning is that adults with severe cerebral palsy often have contractures in many joints and limitations in more than one plane of movement. Hip motion, for example, typically is restricted in abduction, lateral rotation, and extension.11,16 Another problem is that the severity of the contractures can limit positioning options, such as standing. Passive range of motion (PROM) exercises are interventions that are used for contractures of any severity and all limitations of joint PROM. Although some authors have proposed that PROM exercises are ineffective18 (an opinion that is supported by the studies showing prolonged elongation to be necessary5,12–14), other therapists continue to use passive stretching.10,11 In 2 studies, researchers found at least minimal benefits to PROM exercises for young people with cerebral palsy.7,19

Over a 2-year period, McPherson et al7 examined the effects of PROM exercises and positioning on knee flexion contractures of 4 participants between 10 to 18 years of age. During the first year of the study, the participants received PROM exercises 3 times a day at school and twice a week at home. During the second year, PROM exercises at school were discontinued, and participants were positioned in prone and supine standers for 1 hour a day. The PROM exercises continued twice a week at home. The authors compared PROM measurements for periods of treatment (when school was in session) with PROM measurements for periods of nontreatment (Christmas and summer vacations). The participants' PROM measurements increased during the 2 school semesters of the first year and the fall semester of the second year, and they decreased during 3 of the 4 nontreatment periods. The average increase over the year was 4 to 9 degrees, and the average decrease during nontreatment times was 5 to 10 degrees.

Miedaner and Renander19 studied 13 participants who were 6 to 20 years of age and assigned the participants to 1 of 2 groups. For 5 weeks, one group received PROM exercises 5 consecutive days a week, and the other group received PROM exercises 2 nonconsecutive days a week. For the next 5 weeks, the frequency of exercise was reversed for the 2 groups. Changes in PROM measurements averaged plus or minus 2.5 degrees. Frequency of PROM exercises made no difference in 6 of the 7 lower-extremity measurements. Straight leg raising on the right side was greater under the 5-day-per-week condition than under the twice-a-week condition. As was the case in the study by McPherson et al,7 participants received positioning and bracing in the classroom and PROM exercises at home throughout the study, which makes the contribution of the PROM exercises unclear.

Although research supporting the effectiveness (or ineffectiveness) of PROM exercises is limited, we have observed that PROM exercises are commonly used interventions for adults with cerebral palsy in institutions and community-based programs. These exercises usually are carried out by staff who have been taught by physical therapists to do the exercises during times set aside for exercise or during daily activities (eg, dressing, bathing). Although the performance of PROM exercises often continues for years, we have observed few attempts to determine whether they are effective. A single-subject research design is one method of gathering evidence in clinical settings to determine whether an intervention is effective.20 We used a single-subject research design for this study to examine the effect of PROM exercises on lower-extremity PROM measurements of 6 adults with cerebral palsy.

Method

Participants

Six adults (4 men and 2 women; X̄=31 years of age, range=20–44 years) with spastic quadriplegic cerebral palsy participated in the study. See Table 1 for descriptions of the participants. All participants lived in a state-operated residential facility for people diagnosed with mental retardation. A physician and the first author (SLC) selected participants based on 4 criteria: (1) having a legal guardian who could be contacted and who was willing to sign the informed consent form, (2) presence of lower-extremity contractures measuring 20 degrees or greater in at least 3 of the joint motions measured in the study (ie, hip extension, hip abduction, hip lateral rotation, knee extension, and ankle dorsiflexion),13 (3) use of a wheelchair as the primary means of mobility, and (4) current or previous participation in a physical therapy program. Exclusion criteria were: (1) a history of resisting PROM exercises to the extent that full PROM was rarely, if ever, achieved, as judged by the first author, (2) a medical condition that might have prevented the participant from completing the study, (3) a diagnosis of arthritis or other joint disease, (4) lower-extremity orthopedic surgery within 2 years of the beginning of the study, and (5) a windswept hip deformity (limitations of adduction and medial rotation of one hip and limitation of abduction and lateral rotation of the opposite hip21) that prevented positioning for goniometric measurements.

We planned the study to be a single-subject, multiple-baseline design with 6 participants, 3 of whom received PROM exercises (group 1) and 3 of whom had not received PROM exercises for at least 6 months before the start of the study (group 2). All participants had previously received PROM exercises and developmental therapy for many years, but PROM exercises had been discontinued for group 2 participants after they demonstrated fairly stable PROM measurements over time, as determined by annual physical therapy examinations. We wanted to know whether the PROM of participants who were receiving PROM exercises would change when the exercises were discontinued and whether the PROM of participants who had not been receiving the exercises would change when exercises were provided.

Table 1 lists characteristics of the 6 participants. All were diagnosed as having mental retardation, but the true abilities of people with severe cerebral palsy and limited communication skills can be difficult to measure. The musculoskeletal status and functional abilities of the 2 groups were similar, but the average age of the group 1 participants was 25 years (range=20–32 years), and the average age of the group 2 participants was 36 years (range=32–44 years). The older age of the group 2 participants probably contributed to the decision to discontinue their PROM exercises, which had occurred before the first author started working at the institution. These 6 participants were selected for the study because they were the first people who met the inclusion criteria and whose legal guardians provided us with informed consent.

Design

The study consisted of 2 multiple-baseline designs, each with 3 participants.22 During phase A, group 1 participants, who had been receiving PROM exercises 3 times per week, continued to receive PROM exercises. During phase B, PROM exercises were discontinued. Group 2 participants received no PROM exercises during phase A, and PROM exercises were provided during phase B.

As is customary in multiple-baseline designs, the duration of each phase for each participant was individualized, and the initiation of phase B was staggered across the participants as each participant's PROM measurements became stable.22 For the majority of the joints measured, PROM measurements were considered stable when they were within 5 degrees of each other23 over a period of at least 3 out of 4 weeks. Stability, or a stable trend (increasing or decreasing measurements at a constant rate of change) over a period of 3 out of 4 weeks, was the criterion for discontinuing PROM exercises for group 1 participants or for beginning PROM exercises for group 2 participants. All participants were measured each week for 16 consecutive weeks. Phase A measurements for group 1 participants were established after 5 weeks for participant 1A, after 8 weeks for participant 1B, and after 11 weeks for participant 1C. For group 2 participants, phase A measurements were established after 4 weeks for participant 2A, after 8 weeks for participant 2B, and after 11 weeks for participant 2C.

Passive Range of Motion Program

The independent variable was a PROM exercise program for the joint motions of hip extension, hip abduction, hip lateral rotation, knee extension, and ankle dorsiflexion. The first author instructed physical therapy aides in the PROM exercise protocol. Instruction included verbal explanation, demonstration, observation of the aides performing each exercise, feedback on their performance, and written instructions with pictures illustrating how to perform each exercise. The exercises were based on PROM exercises published by Bezner24 and Kisner and Colby.25 For each of the participants, the investigator monitored one exercise session a week throughout the study to ensure that the physical therapy aides adhered to the protocol.

The protocol was based on 2 studies in which the effectiveness of PROM exercise for young people with cerebral palsy was studied.7,19 In both studies, the PROM exercises consisted of moving an extremity passively to the end of the PROM and holding this position for 20 to 60 seconds, then repeating this stretch 5 times. Researchers studying people with and without neuromusculoskeletal impairments have found that one 30-second stretch 5 days a week is as effective in increasing hamstring muscle length as one 60-second stretch or three 30- or 60-second stretches.26,27 Based on our experience with people with cerebral palsy, however, we believe that more than one repetition is beneficial because resistance to passive stretch seems to decrease with repetition.

The aides performed 5 repetitions of each passive joint motion, holding the position at the end of the range for 20 seconds during each repetition. They were instructed to move the joint only to the point of resistance and to avoid forcing the movement. They also were given instructions for obtaining as much motion as possible, such as moving slowly, providing a gentle continuous stretch, avoiding pressure on the balls of the feet or palms of the hand, and bending an adjacent joint if movement was difficult to initiate.

The aides could do the 5 exercises in any order that they chose. Participants were placed in a supine position for all exercises except hip extension. For the hip extension exercise, participants were positioned prone with their hips at the edge of the table. The aides' hand placements were done as illustrated in Bezner.24

The PROM exercise sessions were carried out 3 times per week. Each session lasted for approximately 30 to 45 minutes, including time for transferring, positioning, and talking with the participant. In the studies26,27 of people without neuromusculoskeletal impairments, the researchers did not examine frequencies other than 5 days per week. They provided no rationale for using this frequency. We selected a frequency of 3 days per week because, in our experience, it is a frequency often used for adults with cerebral palsy living in institutions and because Miedaner and Renander19 found that PROM did not differ when their participants received PROM exercises 2 times a week or 5 times a week.

Goniometric Measurements

Our study's dependent variables were bilateral goniometric measurements of hip extension, hip abduction, hip lateral rotation, and ankle dorsiflexion as well as 2 measurements of knee extension: one with the hip flexed and the other with the hip extended. Measurements were taken each week using a 30.48-cm (12-in) plastic goniometer with a 360-degree scale. Although the reliability of goniometry for measuring joint limitations due to contractures has been questioned,28,29 investigators often have used a goniometer to measure the joint PROM of people with cerebral palsy.7,19 To promote consistency in measurements, the 16 measurement sessions for each participant were done on the same day of the week and at the same time of day, with the participant lying on a firm, vinyl-covered, high-low mat table. Semipermanent marks were made on each participant's bony landmarks with a laundry marker to identify the goniometer's fulcrum, stationary arm, and measurement arm positions. Color photographs of the measurement positions and specific written instructions for the 6 joint motions were available for the aides and therapists to review throughout the study.

When measuring each joint motion, the first author, designated as therapist 1, moved the extremity passively through the full available PROM for 3 repetitions. A slow 30-second stretch was applied on the third repetition to “differentiate a reflex or active muscle contraction from the structural limitation of the muscle, tendon, or joint capsule.”29(p661) This procedure was intended to minimize resistance to passive stretch and identify the end of the PROM. The joint PROM was measured at the end of the 30-second stretch by an occupational therapist (therapist 2). Although having someone other than the principal investigator move the limb through the PROM (to control for potential bias) would be the preferred method, another person with the necessary skill was not available for the number of measurement sessions required. To help control for bias, therapist 2 was not informed of the participants' group assignments and their progress within and between the phases of the study.

The testing sequence was consistent for every measurement session,30 and the procedures for positioning and hand placement were standardized for each joint motion.31 First, each participant's right lower extremity was measured in the following order: (1) knee extension in the supine position with the hip extended29; (2) knee extension in the supine position with the hip flexed to 90 degrees, as indicated by a goniometer that was fixed at 90 degrees and positioned on the mat table at the level of the greater trochanter19; (3) ankle dorsiflexion in the supine position with the knee extended and the calcaneus in as neutral a position as possible in an attempt to distinguish between ankle and forefoot motion29; (4) hip abduction in the supine position with the hip extended and the lower leg positioned off of the end of the table32; (5) hip lateral rotation in the supine position with the lower leg positioned off of the end of the table28; and (6) hip extension in the prone position with the hips at the edge of the table, the pelvis level, and the knee flexed.33 While the participant was positioned prone, left hip extension was measured. Then, the remaining left lower-extremity joints were measured in the same order as the joints of the right lower extremity. Because all of the participants had knee flexion contractures and because of the importance of knee extension with hip flexion for wheelchair seating, knee extension was measured with the hip extended as far as possible and with the hip flexed to 90 degrees. Flexing the hip to 90 degrees also was intended to control any effects on knee PROM if hip extension changed over the course of the study.

Reliability

To determine interrater reliability, approximately 18% of the measurements, including 2 or 3 measurement sessions per participant, were repeated independently by another physical therapist (therapist 3) throughout the duration of the study. Therapist 3 participated only in the reliability study and did not know the participants' group assignments and progress. Therapist 3 followed the measurement protocol while therapist 1 (the first author) measured the joint PROM. Therapist 1 used a goniometer that was masked on one side with paper to prevent her from seeing the result until after therapist 2 (the occupational therapist) had recorded each measurement.34 Before the study was initiated, the 3 therapists practiced the measurement, positioning, and stretching techniques until they achieved agreement within 5 degrees per joint measurement. We chose to determine interrater reliability rather than intrarater reliability because (1) we were concerned that memory would affect 2 trials by one rater separated by a short interval and (2) if interrater agreement was acceptable, intrarater agreement also was likely to be acceptable.

Reliability was represented by an intraclass correlation coefficient (ICC), model 3,1.22,35Table 2 shows that coefficients were between .785 for right hip lateral rotation and .988 for right knee extension with the hip flexed to 90 degrees.

Data Analysis

The goniometric measurements collected over the course of the study were recorded on 12 graphs for each participant (one graph for each of the 6 right and left joint motions), for a total of 72 graphs. The graphs were oriented to show an increase in PROM when the data points went in an upward direction and a decrease in PROM when they went in a downward direction.

We first analyzed the graphed data through visual analysis, a traditional method of interpreting single-subject research,36 to determine whether PROM improved, decreased, or did not change across the 2 phases. Through visual analysis, investigators look grossly at level, trend, variability, and slope of the graphed data.37 We used trend data more than level data because changes in level (eg, rapid change in PROM) were not expected and were due possibly to measurement error. We also used visual analysis of trends in conjunction with phase values and changes in slope between phases to determine trend change scores (eg, a joint motion with a low trend phase value [3 or less] and a low slope [approximately 1.0 to 1.05] indicated no change). We disregarded outlier data points (defined as a data point that was 20 degrees greater than or less than the data points immediately before and after it) if at least 5 other data points were available in that phase, and we considered data that remained consistently variable across phases to demonstrate no change.

Investigators have noted that visual analysis alone may lead to inconsistent results.38,39 For this reason and because small treatment effects were expected,37 we also used the C statistic to further analyze the data.40,41

Nourbakhsh and Ottenbacher42 used 3 statistical methods for single-subject data—the split-middle method of trend estimation, the two-standard deviation bandwidth method, and the C statistic—to analyze the same 42 graphs. They found somewhat different results using each method and concluded that researchers should use several approaches to analyze single-subject data, one of which should be visual analysis. We chose the C statistic as the other method because many of the graphs showed a visually obvious trend, which made the two–standard deviation bandwidth method inappropriate,42 and because the split-middle method of trend estimation often is inconsistent with visual analysis.

With the C statistic, phase A data are analyzed first to determine whether a statistically significant trend exists. Statistical significance is determined by dividing C by its standard error, which gives a z value that can be interpreted using the normal probability table for z scores.40,42 If a trend is not found, the phase B data are appended to the phase A data, and the combined data are reanalyzed using the same procedure. If a trend is found in the phase A data, a less powerful alternative procedure can be used to construct separate data series from phase A and phase B data and to compare them. A significant z score indicates that the trend in phase A and phase B are different.40 We used a 1-tailed test with an alpha of .05 (z≥1.645). The unidirectional hypothesis was that PROM would be greater during the phase in which PROM exercises were provided.

Results

Group 1

Table 3 shows the means, standard deviations, visual analysis results, and z values of the 36 graphs for group 1 participants. This group received PROM exercises during phase A and PROM exercises were discontinued during phase B.

Goniometric Data (in Degrees) for Group 1 Participants Who Received Passive Range of Motion (PROM) Exercises During Phase A and Did Not Receive PROM Exercises During Phase B

Visual analysis of the data of participant 1A indicated no change in PROM between phase A and phase B for 10 of the 12 joints measured. The rate of increase in left hip extension decreased during phase B and a downward trend occurred in right ankle dorsiflexion during phase B. Both observations were supported by the z values. The z values also indicated a difference between phases in bilateral hip lateral rotation and knee extension with the hip flexed 90 degrees. Visual analysis indicated that the reason for the discrepancy was probably the increasing trend during the relatively short phase A, which leveled off during phase B.

Visual analysis of participant 1B's data identified no change in 7 of the 12 measurements. Right and left hip lateral rotation showed a downward trend in phase B and ankle dorsiflexion decreased bilaterally during phase B. Left hip abduction increased during phase B. The z values supported a difference in these 5 measurements. The z values also indicated a difference in right and left knee extension with the hip flexed 90 degrees, which visual analysis had not revealed. We examined the graphs again to try to determine the reason for the discrepancy and saw that PROM increased during phase B (also indicated by the means), but not enough to say with any confidence that a difference existed. The z values could not support a difference because we used a 1-tailed test, and the direction of any difference was in the opposite direction.

Visual analysis of participant 1C's data showed no difference in PROM between phases for 9 of the 12 measurements. During phase B, right hip lateral rotation and right knee extension with the hip flexed 90 degrees decreased. This finding was supported by the z values. Visual analysis indicated that left hip abduction increased during phase B. The visual analysis did not support the z values, which indicated a difference in right hip extension and left knee extension with the hip flexed 90 degrees. Reinspection of the graphs again indicated no change, which was supported by the mean PROM during the 2 phases. The long baseline with an increasing trend in the baseline data may have affected the C statistic results.

Group 2

Table 4 shows the means, standard deviations, visual analysis results, and z values for the 36 graphs for group 2. Group 2 participants did not receive PROM exercises during phase A and PROM exercises were provided during phase B.

Goniometric Data (in Degrees) for Group 2 Participants Who Did Not Receive Passive Range of Motion (PROM) Exercises During Phase A and Received PROM Exercises During Phase B

Visual analysis of the data for participant 2A showed no change in 7 of the 12 PROM measurements. Visual analysis indicated an increase in 2 measurements during phase B: left knee extension with the hip extended and left knee extension with the hip flexed 90 degrees. The z values supported these 2 observations and indicated no other increases in PROM during phase B. Visual analysis indicated a decrease in 3 measurements when PROM exercises were provided during phase B: right hip extension, right knee extension with the hip extended, and right ankle dorsiflexion.

Visual analysis of participant 2B's data indicated no change in 8 of the 12 measurements. Visual analysis showed a negative change in 4 measurements during phase B: bilateral hip lateral rotation and dorsiflexion. No positive changes were identified with visual analysis or the z values.

Visual analysis of the data of participant 2C indicated no change in 8 of the 12 PROM measurements. A negative change was observed during phase B in 3 PROM measurements: bilateral hip lateral rotation and right ankle dorsiflexion. Visual analysis and the z value indicated an increase in right hip abduction during phase B.

In summary, visual analysis of the grouped data for the subjects in group 1 showed no change in 28 of 36 joints when PROM exercises were discontinued. Visual analysis showed decreased PROM in 8 joints, results that the z values supported. Visual analysis also showed an increase in PROM for 2 of the 36 joints after PROM exercises were discontinued. The z values indicated a decrease in 4 joint PROM measurements when PROM exercises were discontinued, which was not supported by visual analysis.

Visual analysis of the data of all 3 subjects in group 2 showed no change in PROM for 23 of 36 joints when PROM exercises were provided. Visual analysis and the z values indicated an increase in PROM in 3 joints when PROM exercises were provided during phase B. Visual analysis indicated a decrease in 10 measurements during phase B.

Discussion and Conclusions

For both groups of participants, our results showed no consistent differences in lower-extremity PROM measurements when the participants received and did not receive PROM exercises. Most of the participants demonstrated a gradual increase in PROM in phase A and showed little change in motion during phase B, regardless of whether PROM exercises were discontinued or provided during phase B. As a result of the study, PROM exercises were discontinued for all participants.

The gradual increase in PROM during phase A appeared to be the result of the participants' increasing cooperation with the person taking the PROM measurements over the first few weeks of the study. Although an exclusion criterion was resistance to PROM to an extent that joint range could not be achieved, the participants did appear to guard against full PROM initially. The participants also demonstrated week-to-week variability in measurements that we believe were unlikely to be related to real change in joint PROM.

We are not aware of research that has examined consistency of goniometric measurements of adults with spastic quadriplegic cerebral palsy; however, Harris and colleagues43 found wide daily variations when measuring a child with spastic quadriplegia, and they concluded that a change of 10 to 15 degrees may not represent real change. We contend that our interrater reliability estimates were excellent to good; however, we assessed reliability by having 2 therapists measure the participants on the same day, one immediately after the other. Day-to-day variation in participants would not have been affected by—or detected by—our method. Future research to examine test-retest reliability of goniometric measurements of adults with spastic quadriplegia and cognitive impairments, with time between measurements, could be useful.

Despite the variability of our measurements, we showed that, for the 6 adults with cerebral palsy, PROM exercises did not appear to generally affect lower-extremity goniometric measurements over a 16-week period of time. A limitation of our study was that all participants did not receive the same amount of PROM exercises. The staggered phase A and 16-week available time frame meant that participants received from 5 to 12 weeks of PROM exercises. The results, however, are consistent with the views held by some authors18,44 that passive exercise is not effective in the management of contractures associated with cerebral palsy. The results are not consistent with the results of the studies by McPherson et al7 and Miedaner and Renander,19 who found modest PROM increases following PROM intervention.

One reason for the inconsistency may be the age of the participants. Our participants were between 20 and 44 years of age, and their contractures could have been less responsive to change than participants in the other studies who were between 6 and 20 years of age. Another difference in the studies is that their participants received positioning and other co-interventions, which our participants did not receive. These co-interventions, rather than the PROM exercises, could have been responsible for the change.

The studies also differed in the number of participants, the length of the intervention, the joints investigated, and the research design. McPherson et al7 used a group design to study knee extension of 4 participants over a 2-year period. Miedaner and Renander19 also used a group design and studied the hip, knee, and ankle PROM of 13 participants over 10 weeks. Our study was similar to these previous studies in the limited number of participants, but our use of a single-subject design enabled us to analyze the effects of intervention for each participant, which the group designs do not permit. Some of the participants in the previous studies may not have benefited from the intervention, but the analyses of group data would have obscured the individual effects.

The amount of PROM exercise also may have contributed to lack of changes in the measurements. Although the PROM protocol was based on the literature related to people with cerebral palsy,7,19 research with people without neuromusculoskeletal deficits indicate that stretching for one 30-second stretch 5 times per week is effective.26,27 Although this amount cannot be generalized to people with neuromusculoskeletal impairments, it may be worth investigating. Another consideration is the length of the intervention. Our 16-week study may not have been long enough to show an effect of PROM exercises or an effect of discontinuing them.

The results of our study cannot necessarily be generalized to other adults with cerebral palsy, particularly those with characteristics that differ from those of our participants. The external validity of single-subject research is demonstrated by replication,22 and our design and methods lend themselves well to the clinical setting and could be used by other clinicians to determine whether PROM exercise is effective for individual clients. Replication of the study with other people with similar characteristics also would broaden its applicability.22 For future studies, a larger number of data points and a more stable baseline could improve the accuracy of the analyses.

Measurement and treatment of contractures will continue to be important for adults with cerebral palsy to address potential deterioration, overuse syndromes, and joint deterioration.1 Physical therapy programs that focus only on PROM, however, should be reconsidered because both the clinical usefulness and social validity45 of this intervention are questionable. Social validity is a term used in applied behavior analysis, from which single-subject research developed. It refers to the social importance of treatment goals and procedures, and the person's satisfaction with them. Intervention, we believe, must go beyond the person's secondary impairments to address functional limitations and ability to fulfill life roles.46 Future research, in addition to attempting to answer continuing questions about the effectiveness of various techniques for increasing PROM measurements, needs to address questions about relationships between joint PROM and functional capabilities. Even if a technique is shown to increase PROM, we need to know whether the increase affects the ability of an adult with cerebral palsy to function or makes an important difference in the ease of caregiving.

Footnotes

All authors provided concept/research design and data analysis. Ms Cadenhead and Dr McEwen provided writing. Ms Cadenhead provided data collection and project management, and Dr McEwen provided fund procurement. The authors thank the occupational therapist who helped with data collection, the physical therapist who participated in the interrater reliability study, and the participants' physician who assisted with the study.

This study was conducted in partial fulfillment of the requirements for Ms Cadenhead's postprofessional Master of Science degree from the University of Oklahoma Health Sciences Center. The study was approved by the University of Oklahoma Health Sciences Center Institutional Review Board and by the Human Rights Committee of the Northern Oklahoma Resource Center.

The study was partially supported by Preparation of Related Services Personnel grants H029F00056 and H029F30020 from the US Department of Education, Office of Special Education and Rehabilitative Services. This article, however, does not necessarily reflect the policy of that office, and official endorsement should not be inferred.